1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition. More particularly, the present invention relates to a radiation-sensitive resin composition suitably used as a chemically-amplified resist useful for microfabrication utilizing various types of radiation such as deep ultraviolet rays such as a KrF excimer laser, ArF excimer laser, or F2 excimer laser, X-rays such as synchrotron radiation, and charged particle rays such as electron beams.
2. Description of Background Art
In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to increase the degree of integration.
In a conventional lithographic process, near ultraviolet rays such as i-line radiation have been used. However, it is difficult to perform microfabrication with a line width of sub-quarter micron using near ultraviolet rays.
Therefore, in order to enable microfabrication with a line width of 0.20 μm or less, utilization of radiation with a shorter wavelength has been studied. As examples of radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), and an F2 excimer laser (wavelength: 157 nm) have attracted attention.
As a resist suitable for irradiation by an excimer laser, a number of chemically-amplified resists utilizing a chemical amplification effect caused by a component having an acid-dissociable functional group and a component which generates an acid upon irradiation (hereinafter referred to as “exposure”) (hereinafter referred to as “photoacid generator”) have been proposed.
Japanese Patent Publication No. 2-27660 discloses a chemically-amplified resist containing a polymer having a t-butyl ester group of a carboxylic acid or t-butylcarbonate group of a phenol, and a photoacid generator. This resist utilizes a phenomenon in which a t-butyl ester group or a t-butyl carbonate group contained in the polymer dissociates by the action of an acid generated upon exposure to form an acidic functional group such as a carboxyl group or a phenolic hydroxyl group, whereby the exposed region of the resist film becomes readily soluble in an alkaline developer.
Generally, conventional chemically-amplified resists contain a phenol resin as a base resin. However, since deep ultraviolet rays used as radiation are absorbed due to the presence of aromatic ring in the resin, a sufficient amount of deep ultraviolet rays cannot reach a lower portion of the resist film. Therefore, the irradiation dose is increased in the upper portion of the resist film and decreased in the lower portion. As a result, the resist pattern after development is in the shape of a trapezoid in which the resist pattern is thinner in the upper portion and thicker in the lower portion, whereby sufficient resolution cannot be obtained. If the resist pattern after development is in the shape of a trapezoid, desired dimensional accuracy cannot be achieved in a succeeding step such as an etching step or ion implantation step. Moreover, if the shape of the upper part of the resist pattern is not rectangular, the rate of removal of the resist by dry etching is increased, whereby it is difficult to control etching conditions.
The shape of the resist pattern can be improved by increasing the radiation transmittance of the resist film. For example, a (meth)acrylate resin represented by polymethylmethacrylate is a desirable resin from the viewpoint of radiation transmittance because the (meth)acrylate resin has high transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 4-226461 discloses a chemically-amplified resist using a methacrylate resin, for example. However, this composition has insufficient dry etching resistance due to the absence of an aromatic ring, although the composition excels in microfabrication performance. This makes it difficult to perform etching with high accuracy. Therefore, a composition having both transparency to radiation and dry etching resistance cannot be provided.
As a means to improve dry etching resistance of the chemically-amplified resist without impairing transparency to radiation, a method of introducing an aliphatic ring into the resin component in the resist instead of an aromatic ring is known. For example, Japanese Patent Application Laid-open No. 7-234511 discloses a chemically-amplified resist using a (meth)acrylate resin having an aliphatic ring.
This resist uses a group which comparatively easily dissociates by the action of a conventional acid (acetal functional group such as a tetrahydropyranyl group), or a group which comparatively scarcely dissociates by the action of an acid (t-butyl functional group such as a t-butyl ester group or t-butylcarbonate group) as the acid-dissociable functional group in the resin component. However, in the case of using the resin component containing the former acid-dissociable functional group, although the resist excels in basic properties such as sensitivity and pattern shape, storage stability as a composition is insufficient. In the case of using the resin component containing the latter acid-dissociable functional group, the resist exhibits insufficient basic properties such as sensitivity and pattern shape, although storage stability as a composition is excellent. Moreover, since the aliphatic ring is introduced into the resin component in this resist, hydrophobicity of the resin is considerably increased. This results in insufficient adhesion to a substrate.
When forming a resist pattern by using a chemically-amplified resist, a heat treatment is usually performed after exposure in order to promote the dissociation of the acid-dissociable functional group. The line width of the resist pattern is inevitably changed to some extent as the heating temperature is changed. However, in order to deal with a recent decrease in size of integrated circuit devices, development of a resist which shows only a small change in line width due to a change in heating temperature after exposure (specifically, temperature dependency) has been demanded.
As a means to improve properties of a chemically-amplified radiation sensitive composition as a resist, a number of multi-component compositions containing three or more components to which a high-molecular-weight or low-molecular-weight additive is added have been proposed. For example, Japanese Patent Application Laid-open No. 7-234511 discloses that effects of post exposure delay from exposure to heat treatment are reduced by adding t-butyl 3-adamantanecarboxylate as a hydrophobic compound to a resist containing a p-hydroxystyrene copolymer such as a copolymer of p-hydroxystyrene and tetrahydropyranyl (meth)acrylate or t-butyl (meth) acrylate or a copolymer of p-hydroxystyrene and p-tetrahydropyranyloxycarbonyloxystyrene or p-t-butoxycarbonyloxystyrene as a resin having a hydrophilic group, and that stable patterning can be performed even in the case of a resist containing a group having strong hydrophobicity.
However, conventional multi-component chemically-amplified radiation sensitive compositions including the composition disclosed in Japanese Patent Application Laid-open No. 7-234511 show a large amount of change in line width of the line pattern depending on the density of the line and space pattern. Therefore, the performance as a resist of these compositions is not satisfactory.
In view of the above-described situation, in order to develop technology capable of dealing with the progress of miniaturization and an increase in the application field of integrated circuit devices, development of a chemically-amplified resist which is applicable to short wavelength radiation represented by deep ultraviolet rays, shows only a small change in line width of the line pattern depending on the density of the line and space pattern, and excels in transparency to radiation, sensitivity, resolution, and the like has been strongly demanded.
Accordingly, an object of the present invention is to provide a radiation-sensitive resin composition useful as a chemically-amplified resist capable of forming a minute line pattern even if the width of the space of the line and space pattern is increased, and excelling in transparency to radiation, sensitivity, resolution, and the like.